You just bought your first home. Congratulations: You're an adult! Now it's time to fill it up. But if you were planning to pack up those ratty old beanbag chairs and the bed that awakens you with a morning backache and move them to your new place, we have a few suggestions. It's time for a grown-up upgrade. Here's where to start.

Invest in the important staples

You can scrimp on your mattress because it's not something that guests will see, right? Not so fast. A good mattress should be at the top of your list because it affects something more important than the opinions of friends and family: Your health.

"You wouldn't run a marathon or hike a mountain without the right gear. And yet, despite spending a third of our lives sleeping, many of us haven't adequately prepared in the bedroom - when it comes to mattresses, that is," said Huffington Post. "You might be tempted to blame your budget for continuing to doze on a less-than-ideal mattress, but considering just a little bit more shut-eye can help you lose weight, improve your memory and live longer, can you really put a price tag on good sleep? But the wrong mattress - or the mattress that's simply too old - can be the cause of more than that crick in your neck or your lower back pain. Here are five sneakier ways your mattress affects your sleep - and your health.

If you just can't bring yourself to spring for that kind of big-ticket item right now, look for opportunities to spread out payments with a zero percent interest deal, which more and more retailers are offering. Go to a place like Rooms to Go and you might be able to get your mattress and a living room set with monthly payments that are right around what you and your honey would pay for a nice lunch.

Measure, measure, measure

Having furniture that's too small or too large for a room can make it function poorly and look "off." Measure ahead of time so you know what to look for. Stores like HomeGoods have stacks of paper measuring sticks laying arouond, but you won't always be that lucky. Measure your space and input everything in your phone, stash a measuring tape in your bag, and you won't have to guess if something will work when you're out shopping.

Dress up the bed

One of the best ways to make a bedroom look pulled together is with a headboard. But many people don't even take a look at options because they assume they will be too expensive. You can get a super chic headboard for a minimal spend if you know where to go. This tufted headboard from Overstock looks like it would cost you about as much as a monthly mortgage payment, but it's just $137.

Buy a decent couch

The couch falls squarely under that "investment pieces" category. It will probably be among your most-used pieces of furniture, so it needs to be able to stand up to a lot of butts, a few feet, an assortment of overnight guests, and maybe a spill here and there. Comfort is key, and so is durability.

You'll hate yourself - and your couch - if you buy super cheap just to get something in the room. And we're speaking from experience. Our first cheapie couch (purchased online, BTW) started falling apart after about a month. Contrast that against what Sotheby's-trained home shopping expert Jennifer Litwin, author of Best Furniture Buying Tips Ever, says should be the lifespan of the couch: "The general prognosis is about 10 to 15 years, she told The Nest. You can scrimp on other, easily replaceable items like side tables and chairs that won't be used often, but when it comes to that couch: Go ahead and splurge a little.

Like and follow influential sites

Speaking of chairs…

Just today we learned about this great-looking $43 chair on Amazon that we never would have known about if we weren't fans of MyDomaine. And, by fans, we mean we follow them on Facebook. "The midcentury-modern chairs feature velvet upholstering, steel legs, and are available in dusty rose, moss green, gray-green, and teal, to name a few," they said. They're sold in a set of two, starting at $85."

Sites like Apartment Therapy and Design Sponge are great places to get interior design ideas, and liking and following a few favorite stores like World Market and HomeGoods and online sites like Wayfair and One Kings Lane is a great way to keep up to date on sales and trends.

Be careful about buying online

When comfort and quality are key, you want to be careful about buying without being able to see, touch, and sit. If you just have to have it, at least you can read what others have to say before producing your credit card. Back to that $43 chair from Amazon: "How do you know if chairs sold on Amazon look and feel as luxe in real life," asked MyDomaine. "Members of the Facebook group purchased the chairs and posted images of the items IRL, confirming that they live up to the hype. Yes, if the long chain of comments, likes, and photos are any indication, this might be one of Amazon's best-kept secrets."

Buy some art

Real art, from real actual artists. You can find some surprisingly affordable pieces that will give your home a personal touch. "Collecting art can be an expensive habit, but these days there are plenty of places to get amazing original art for a great price," said POPSUGAR. Like Minted, one of our favorite spots for original art that "discovers talent through ongoing design competitions. Designers submit, the Minted community votes to tell them what to sell, and we end up with seemingly limitless options at super affordable prices," they said.

That doesn't mean you need to give up all your posters (although, we adults call them "art prints.") Just get them framed nicely. "Luckily, framing has never been easier, now that there are online services like Framebridge," said Refinery29. "And when all else fails, you can't go wrong with the basic Ikea RIBBA frames (just make sure the art fits and doesn't slip and slide around when it's hanging on the wall)."

Don't be afraid to go to IKEA

IKEA is good for more than frames, even though you probably equate grown-up furniture with stuff you don't have to put together yourself. But not everything has to be a permanent fixture when you're just starting out. Concentrating on the big-ticket items may leave limited funds available to fill in the rest of your place. Many a new homeowner has hit the big blue-and-yellow warehouse and headed straight for the MALM dresser. It's cheap (starting at $54 for a two-drawer version), it's functional, and if you have a little bit of creativity—or the ability to do some basic research and follow directions—you can turn it into something that looks far more expensive.

We're also loving this South Shore Cookie 6-Drawer Double Dresser in gray and white from Walmart, which could give you the function in you need in an extra bedroom or guest room with a sleek, modern look. We guarantee your guests will never know where it came from…unless they were savvy enough to purchase on for their own home.

Get a few key housewares

Living like an adult isn't just about what you put stuff on. It's also about the stuff you put on you. Still using the same stiff sheets you bought for your first apartment or ratty towels you'd be embarrassed for company to see? "You'll feel more grown-up the second you stop drying off your body with a towel that has a fish in sunglasses on it," said Refinery29."